Method of producing fiber pulp from vegetable of fibrous material

ABSTRACT

The invention relates to the production of fiber pulp from fibrous vegetable material by a process generally comprising the steps of preheating the starting material in a closed receptacle by means of steam and thereafter grinding said preheated material between the grinding discs enclosed in a casing of a grinding apparatus under superatmospheric pressure. As the pressure in the preheating receptacle during the whole treatment of the material must exceed the superatmospheric pressure in the grinding apparatus proper in order to prevent back flow of steam and material, the invention provides novel means for maintaining the pressure difference in consideration by introducing another gaseous pressure agent than steam into the preheating receptacle. This renders possible to keep the starting material in the receptacle at a lower temperature than that corresponding to that of a pure steam atmosphere under the same increased pressure. The additional pressure generated in the preheating vessel by the introduced other gaseous agent also assists in the discharge of the ground produce from the grinding casing upon treatment between the grinding discs. The additional gaseous agent can also be used as a cooling agent. The reduced temperature in the preheating vessel protects the material to be ground, in particular wood chips to be subjected to the so called thermomechanical grinding method, against discoloration and improves also the grindability of said material.

United States Patent [191 Reinhall Oct. 7, 1975 METHOD OF PRODUCINGFIBER PULP FROM VEGETABLE OF FIBROUS MATERIAL Rolf Berti] Reinhall, 16

Killingevagen, S-181 64 Lidingo,

Sweden 22 Filed: Apr.1l, 1974 21 Appl. No.: 459,899

[76] Inventor:

[30] Foreign Application Priority Data Primary Examiner-Granville Y.Custer, Jr. Attorney, Agent, or FirmEric Y. Munson [57] ABSTRACT Theinvention relates to the production of fiber pulp from fibrous vegetablematerial by a process generally comprising the steps of preheating thestarting materialin a closed receptacle by means of steam and thereaftergrinding said preheated material between the grinding discs enclosed ina casing of a grinding apparatus under superatmospheric pressure. As thepressure in the preheating receptacle during the whole treatment of thematerial must exceed the superatmospheric pressure in the grindingapparatus proper in order to prevent back flow of steam and material,the invention provides novel means for maintaining the pressuredifference in consideration by introducing another gaseous pressureagent than steam into the preheating receptacle. This renders possibleto keep the starting material in the receptacle at a lower temperaturethan that corresponding to that of a pure steam atmosphere under thesame increased pressure. The additional pressure generated in thepreheating vessel by the introduced other gaseous agent also assists inthe discharge of the ground produce from the grinding casing upontreatment between the grinding discs. The additional gaseous agent canalso be used as a cooling agent. The reduced temperature in thepreheating vessel protects the material to be ground, in particular woodchips to be subjected to the so called thermomechanical grinding method,against discoloration and improves also the grindability of saidmaterial.

5 Claims, 1 Drawing Figure METHOD OF PRODUCING FIBER PULP FROM VEGETABLEOF FIBROUS MATERIAL BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a method of producing fiber pulpfrom vegetable or fibrous material.

More particularly this invention relates to a method in the productionof fiber pulp from vegetable or iibrous material such as wood chips andcomprising preheating of the starting material in a closed receptacle bymeans of steam and thereafter grinding said material undersuperatmospheric pressure in a grinding apparatus between grinding discsprovided therein.

2. Description of the Prior Art In the prior art preheating processesthe preheating temperature may be below or over 100C, and hitherto thepressure in the receptacle has been adjusted to correspond with thedesired temperature. When the preheated starting material such the chipsare introduced into the grinding apparatus steam is generated during thegrinding between the grinding discs. To prevent back flow of steam intothe receptacle it is obviously necessary to maintain a higher pressurein the receptacle than in the grinding casing.

This is especially valid if a separate gaseous carrier agent, such steamunder pressure, is introduced into the grinding casing to assist in thedischarge of the ground pulp from the casing or an exhaust valveprovided in the outlet thereof as is disclosed e.g. in the commonlyassigned co-pending U.S. Pat. application Ser. No. 299,259, filed Oct.20, 1972, now Pat. No. 3,847,363, issued Nov. 12, 1974 and commonlyassigned co-pending U.S. Pat. application Ser. No. 316,290, filed Dec.18, 1972.

SUMMARY OF THE INVENTION One main object of the invention is to providea method which in a more reliable manner than hitherto renders possibleto maintain a higher pressure in the preheating receptacle than in thegrinding casing.

Another object of the invention is to provide a method which in additionfacilitates the discharge of the pulp ground between the grinding discfrom the casing enclosing said disc.

Still another object of the invention is to provide a method by whichthe properties of the ground produce are improved over the optimumresults obtainable hitherto by a grinding treatment of the kind inconsideration in particular by avoiding the danger of discolor. ation ofthe pulp.

According to one main feature of the invention another gaseous agentthan steam is supplied to the preheating receptacle in order to maintainthe required higher pressure therein. In this manner it is possible toadjust the temperature in the preheater to a level which is mostadvantageous for the starting material e.g. for avoiding discoloringthereof. According to the invention the pressure agent supplied to thereceptacle further has a cooling effect also inside the grinding Zonebetween the grinding discs at the moment when the fibers are uncoveredfrom one another. By applying the invention the quality of the producedpulp, e.g. color and grindability is affected in an favorable manner.The invention is especially applicable to the so called thermomechanical method in which the grinding is effected without assistanceof particular chemicals.

SHORT DESCRIPTTON OF THE DRAWING Further objects, features andadvantages of the invention will become apparent from the followingdescription considered in connection with the accompanying drawing,which diagrammatically in a lateral view shows a plant enabling to carryout the method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingreference numeral 10 denotes a storage bin for the starting materialsuch as wood in disintegrated state or so called chips. The startingmaterial is introduced by a feeding device 12 such as a screw, into avessel or receptacle 14 which is maintained under a predeterminedpressure, the feeding device sealing against said pressure. The vessel14 is at its bottom through a conveyer screw 16 connected to a grindingapparatus 18 of the disc type which comprises a closed casing 20 withinwhich are located a stationary grinding disc 22 and a grinding disc 28mounted within the frame 26 rotatably about a shaft 24. The startingmaterial supplied by the conveyer screw 16 is fed through a centralopening at the inner periphery of an interspace 31 existing between thetwo grinding discs 22, 28. The surrounding grinding casing 20 has e.g.at its bottom an outlet 32 which houses an exhaust valve 34 by which thefree passage area of the outlet is controlled. The outlet 32 may over aduct 36 communicate with a centri-cleaner 38 for separating off thesteam accompanying the ground produce.

Steam under superatmospheric pressure is fed from a pressure source notshown through a pipe 40 to the vessel 14. In this connection a valve 42is mounted in the pipe 40 which valve is actuated by an implement 44sensing the temperature within the zone and a temperature regulatingdevice 46 so that a desired temperature is maintained in the vessel 14.This temperature may be below or over C and may amount to 90 C, forexample. At the same time, a steam pressure at or exceeding atmosphericpressure may prevail in the vessel.

Through a pipe 48, within which a manually or regulator-controlled valve50 is provided, steam can be fed to the grinding casing 20 from the pipe40. The pipe 48 may also include a non-return valve 52.

A pipe 54 from a source (not shown) of compressed air opens into thevessel 14, said pipe housing a valve 56 which controls the supply ofcompressed air to the vessel 41 through an implement 58 sensing thepressure in the interior of the vessel and a regulator 60 for adjustmentto desired pressure in the vessel.

OPERATION OF THE PREFERRED EMBODIMENT The starting material which issupplied to the preheater vessel 14 contains water to 30 60 percent, forexample. This material is preheated inside the vessel to predeterminedtemperature before it is fed by the conveyer screw into the interspace31 between the grinding discs 22, 28. By the grinding work and thefriction heat developed thereby steam is generated. In addition, steamcan be supplied to the casing through the pipe 48 in order to facilitatethe discharge of the final pulp out of the grinding casing. Both thesefactors cause, as is well known, an increase of pressure within thegrinding casing, and in order to prevent steam from penetratingbackwards into the vessel 14 air is now supplied to this latter, so thatrequired excess pressure is obtained by addition of the steam and airpressures in the vessel. In this way a temperature can be maintained inthe vessel which is substantially lower than that which corre sponds toan atmosphere of solely steam at the same pressure. The temperature ofthe starting material or chips in the vessel 14 can now be adjusted inthe most favorable way to prevent discoloration of the chips andtoobtain forced feeding of the introduced starting material through thegrinding interspace 31'. In addition, the supplied air acts as coolingagent during the grinding procedure proper between the grinding discsand has there influence also on the brightness and, otherwise,grindability of the pulp. The grinding can with excellent result beeffected without or with a limited addition of chemicals of conventionaltype such as a mixture of disulphite and sulphite, for example.

Instead of air other gases which do not condense in the vessel or areneutral to the starting material can be utilized as pressure agent inthe vessel 14. The gaseous agent may have a bleaching effect on thechips as is the case with gaseous 80:. The carrier agent supplied underpressure through the pipe 48 need not be steam, but may also beconstituted by air, for example. The invention can to advantage, becombined with the structure which is disclosed in the US. Pat.applications Ser. Nos. 299,259 and 316,290 referred to above.

While one embodiment of the invention has been disclosed and describedwith indication of some possible modifications, it is to be understoodthat thisis for purpose of illustration only, and that the invention isnot to be limited thereby, but its scope is to be determined by theappended claims.

What is claimed is:

1. In a method for producing fiber pulp from fibrous vegetable materialwherein the fibrous material is pre heated in a closed receptacle bymeans of steam and thereafter ground between grinding discs undersuperatmospheric pressure in a grinding apparatus casing communicatingwith the closed receptacle, the improvement comprising the step ofsupplying a gas other i than steam to the closed receptacle at apressure and temperature so as to maintain the total pressure in thepreheater receptacle greater than the pressure in the grinding casingwithout increasing the temperature in the receptacle above thattemperature prevailing therein due to the preheating by steam.

2. The improved method as claimed in claim 11 receptacle by atemperature sensing device,-controlling the supply of steam to thepreheater receptacle in response to the temperature sensed to maintainthe temperature at a desired predetermined level for preheating, sensingthe total pressure in the preheater receptacle and controlling thesupplyof the gas other than steam to the preheater receptacle in response tothe pressure sensed to maintainthe total pressure therein greater thanthe pressure in the grinding casing. 4. The improved method as claimedin claim 1 wherein the gas other than steam supplied to the preheaterreceptacle is one which is capable of bleaching the vegetable fiber.

5. The improved .method as claimed in claim 2 wherein the gasintroducedinto the grinding apparatus casing to further increase the pressuretherein is steam. l l=

1.IN A METHOD FOR PRODUCING FIBER PULP FROM FIBROUS VEGETABLE MATERIALWHEREIN THE FIBROUS MATERIAL IS PREHEATED IN A CLOSED RECEPTACLE BYMEANS OF STEAMS AND THEREAFTER GROUND BETWEEN GRINDING DISCS UNDERSUPERATMOSPHRIC PRESSURE IN A GRINDING APPARATUS CASING COMMUNICATINGWITH THE CLOSED RECEPTACLE, THE IMPROVEMENT COMPRISING THE STEP OFSUPPLYING A GAS OTHER THAN STEAM TO THE CLOSED RECEPTACLE AT A PRESSUREAND TEMPERATURE SO AS TO MAINTAIN THE TOTAL PRESSURE IN THE PREHEATERRECEPTACLE GREATER THAN THE PRESSURE IN THE GRINDING CASING WITHOUTINCREASING THE TEMPERATURE IN THE RECEPTACLE ABOVE THE TEMPERATUREPREVAILING THEREIN DUE TO THE PREHEATING BY STEAM.
 2. The improvedmethod as claimed in claim 1 wherein a gas is introduced into thegrinding apparatus casing to further increase the pressure therein tofacilitate the discharge of ground pulp therefrom further including thestep of maintaining the pressure in the preheater receptacle at apressure greater than the increased pressure in the casing.
 3. Theimproved method as claimed in claim 1 further including sensing thetemperature in the preheater receptacle by a temperature sensing device,controlling the supply of steam to the preheater receptacle in responseto the temperature sensed to maintain the temperature at a desiredpredetermined level for preheating, sensing the total pressure in thepreheater receptacle and controlling the supply of the gas other thansteam to the preheater receptacle in response to the pressurE sensed tomaintain the total pressure therein greater than the pressure in thegrinding casing.
 4. The improved method as claimed in claim 1 whereinthe gas other than steam supplied to the preheater receptacle is onewhich is capable of bleaching the vegetable fiber.
 5. The improvedmethod as claimed in claim 2 wherein the gas introduced into thegrinding apparatus casing to further increase the pressure therein issteam.